Hydrogenation is an established process both in the chemical and petroleum refining industries. Hydrogenation is conventionally carried out in the presence of a catalyst, which usually comprises a metal hydrogenation component deposited on a porous support material. The metal hydrogenation component is often nickel or one or more metals such as platinum, palladium, rhodium or ruthenium.
Hydrogenated derivatives of benzenepolycarboxylic acids or derivatives thereof, such as esters and/or anhydrides, have many uses. Of particular interest is their use as plasticisers for polymeric materials. In this context the dialkylhexahydrophthalates are an example of one class of these compounds that are of particular interest. These materials may be produced by hydrogenation of the corresponding phthalic acid ester in the presence of hydrogen and an active metal hydrogenation catalyst deposited on a support.
In U.S. Pat. No. 5,286,898 and U.S. Pat. No. 5,319,129, dimethylterephthalate is hydrogenated at ≧140° C. and a pressure of from 50 to 170 bar over supported Pd catalysts, which are treated with Ni, Pt and/or Ru to give the corresponding dimethylhexahydroterephthalate. The supports used are alumina of crystalline phase alpha or theta or delta or gamma or beta or mixtures thereof.
In EP-A-0 005 737, aromatic carboxylic esters are hydrogenated at from 70 to 250° C. and from 30 to 200 bar over supported Ni, Ru, Rh and/or Pd catalysts to give the corresponding cycloaliphatic carboxylic esters. The support used is an aluminium oxide of which at least 20% has been converted into lithium-aluminium spinel.
U.S. Pat. No. 3,027,398 describes the hydrogenation of dimethylterephthalate over supported Ru catalysts at from 110 to 140° C. and from 35 to 105 bar. The Ru is deposited on charcoal or kieselguhr.
EP-A 0 603 825 relates to a process for the preparation of 1,4-cycylohexanedicarboxylic acid by hydrogenating terephthalic acid by using a supported palladium catalyst, wherein as support alumina, silica or active charcoal is used.
U.S. Pat. No. 3,334,149 describes a multistage process for the hydrogenation of dialkylterephthalate using a Pd catalyst followed by use of a copper chromite catalyst.
U.S. Pat. No. 5,936,126 describes a process for the hydrogenation of an aromatic compound. The catalyst used contains ruthenium as active metal alone or optionally with one or more other Group IB, VIIB or VIIIB metals on a macroporous support. The macroporous support exhibits an average pore diameter of at least 50 nm and a BET surface area of not more than about 30 m2/g.
U.S. Pat. No. 6,248,924 describes a process for reacting organic compounds. The catalyst used contains ruthenium as active metal alone or optionally with one or more other Group IB, VIIB or VIIIB metals on a support. The support may be a material having macropores (50 to 10000 nm pore diameter) and mesopores (2 to 50 nm pore diameter). In the support 10-50% of the pores are macropores and 50 to 90% of the pores are mesopores. Alumina of surface area (BET) 238 m2/g is specifically exemplified.
Published International Application No. PCT/EP98/08346 (WO 99/32427) describes a process for the hydrogenation of benzene polycarboxylic acids or derivatives thereof. The catalyst used comprises ruthenium as an active metal which is deposited alone or together with at least one other metal of subgroups I, VII or VIII of the periodic table on a support. One of three separate types of support may be used. The first support is macroporous having a mean pore diameter of at least about 50 nm and a BET surface area of at most 30 m2/g. The second support is a material, which has both macropores and mesopores (2 to 50 nm pore diameter), and in which 5-50% of the pores are macropores, 50 to 95% of the pores are mesopores and the surface area of the support is preferably from 50 to about 500 m2/g. The third type of support is a material, which is macroporous and has a mean pore diameter of at least 0.1 lm and a surface area of at most 15 m2/g.
Of particular importance in the hydrogenation of benzenepolycarboxylic acids or derivatives thereof is the degree of conversion of the starting materials and the selectivity of conversion into the desired hydrogenated cyclohexyl derivatives. The degree of conversion should be as high as possible and typically conversion levels of greater than 95% are sought and achieved for these types of hydrogenation. However, in these types of hydrogenation whilst high conversions may be obtained it is difficult to simultaneously achieve the required high degree of selectivity to the desired product. In this regard there is a problem with the generation of low molecular weight and/or boiling point by-products during the hydrogenation reaction. These by-products are often referred to as “lights” and they must be removed from the hydrogenation product before it is used for example as a plasticiser.
There is a need therefore for new hydrogenation processes for the conversion of benzenepolycarboxylic acids or derivatives to the corresponding ring-hydrogenated derivatives, which produce lower levels of “lights” by-products and thus result in improved selectivity for the desired products. It is therefore, an object of the present invention to provide a process for hydrogenating benzenedicarboxylic esters or anhydrides, using specific catalysts, by means of which the corresponding, hydrogenation products may be obtained with high levels of conversion and selectivity.